Hide value from Drop Down List but not delete it

We have an existing drop down list and in that list there is a blue which we do not want users to select in future, however, we wish to retain the historical data for that value. I cannot see any way of doing this other than custom code.

I am not certain which edition of the product you are using, but versions 7.6.x or later of Sugar Enterprise and Sugar Ultimate include functionality called Role-Based Dropdown Lists, which I think would be perfect for your needs.

The Role-Based Dropdown Lists allow you to configure a field's dropdown list so that certain roles can see certain dropdown value options, while hiding others. You could assign each of your users to a role, and then use Role-Based Dropdown Lists to hide the single dropdown value that you do not want them to be able to see. As an administrator, you will still be able to see the value and the full history of that dropdown value will be retained, but your users would not be able to see or select it any longer.

I am not certain which edition of the product you are using, but versions 7.6.x or later of Sugar Enterprise and Sugar Ultimate include functionality called Role-Based Dropdown Lists, which I think would be perfect for your needs.

The Role-Based Dropdown Lists allow you to configure a field's dropdown list so that certain roles can see certain dropdown value options, while hiding others. You could assign each of your users to a role, and then use Role-Based Dropdown Lists to hide the single dropdown value that you do not want them to be able to see. As an administrator, you will still be able to see the value and the full history of that dropdown value will be retained, but your users would not be able to see or select it any longer.

I think Patrick Sullivan's answer should work perfect for your needs but if you prefer do it using custom code you can check this Q/A because it will allow you to hide/show the values of your custom dropdown according to your needs.